Oh man, So may questions, and I have spent too much time on the web... I certainly can not answer everything. But that one deserves it:

I can see all sorts of reasons to up sample to even very extremely high rate than come down (decimate).

One example that comes to mind is that certain types of digital signal processing is very difficult to perform when you are near Nyquist.

Say you have a 44.1KHz system and wish to process (EQ, Reverb and so on) an 20KHz, free of problems. NyQuest is near by at 22.05KHz. So you up sample by X2 (or use 88.2KHz data if already available), and your Nyquist is now at 44.1KHz. Your 20KHz is in a good place now.

Another example: You wish to do a non linear operation, such as a tube sound simulator, fast attack compressor, limiter and so on. Non linear processes will introduce a lot of energy in various places. Well that is fine. A non linear analog, such as a tube, may yield all sorts of sum and differences of frequencies. Even the case of a simple pure tone will. Well, what sounds good in analog may not sound good in digital. Or at least may be very different in digital. Why? In one word, aliasing. There energy produced due to non linearity in analog gear may cover a lot of frequency range, and some of it you don’t hear, because it is just too high for the ear (be it 30KHz or a MHz). But With digital, if you are using say a 44.1KHz converter, all that high frequency stuff re-appears at the audible range.

What if you went to say 88.2KHz sampling? Well, there are 2 frequency regions:

L – the one you hear (say 0-22Khz or so) and H- that you do not hear, 22-48KHz. If anyone wants to move the number 22 up or down be my guest, the concept is still here.

Of course, if one would up-sample by say 64 or 1024… very little gets aliased. And of course one can design the gear (the math) in such a way that you do not need to go that far. Say I want to approximate a non linearity with y=a0+a1*X+a2*X^2, that is a 2nd order curve. I start with a 44.1KHz system (22.05 is the maximum possible tone). The math tells me that no matter how complex the input is, the highest energy produced will be 22.05KHz *2= 44.1KHz.

Nothing will alias if I use 88.2KHz data. But If I wished to process say a 10th order curve, I may have tones 220.5KHz, and thus need a 441KHz data. That is a lot of up-sampling… As always, do not just get to filter things to solve aliasing problems.

I can go on, but hope that what said shows that I am not against working at high rates, when it is needed. We up sample to high rates for DA’s, for processing, for AD input circuits (modulators). There is a whole technology that deal with noise shaping, a tradeoff between few bits at high rates and many bits at low rate. I am all for it. And all of it is about LOCALIZED processes, getting from signal A to signal B the best way, whatever it takes. Non of it conflicts what I said about ridicules it is to use 192KHz for conversion or data format.

Best Regards

Dan Lavry